1. Field of the Invention
The present invention relates to a GaN system compound semiconductor used in a blue laser diode or a blue light emissive diode and a method for fabricating the same, and more particularly, to a GaN system compound semiconductor in which an InxAl1-xN crystal is grown initially on a sapphire substrate as a buffer layer, and a GaN or an InxGa1-xN crystal, GaN system semiconductor, is grown thereon, for improving a surface flatness of the crystal, reducing a stress, and crystal defects; and a method for growing a crystal thereof.
2. Background of the Related Art
GaN or InxGa1-xN crystal, GaN system semiconductor widely used in blue laser diodes or blue light emissive diodes, is fabricated by MOVPE(Metal Organic Vapor Phase Epitaxy) in which an AlN or GaN crystal is grown to a thickness of a few tens of nm at a low temperature of 500 - 600xc2x0 C. on a sapphire(Al2O3) substrate and growing a GaN or InxGa1-xN crystal at an elevated temperature in the vicinity of 1100xc2x0 C. When the AlN or GaN intermediate buffer layer is grown on the sapphire substrate at a low temperature, a rugged columnar AlN or GaN crystal is grown at first, and when a crystal is grown using the irregular columnar AlN or GaN crystal as basis at an elevated temperature, the crystal is grown evenly in a lateral direction, facilitating comparatively flat single crystal growth when the crystal is grown to a certain thickness. The GaN or InxGa1-xN crystal growth on the AlN or GaN intermediate buffer layer grown at a low temperature has advantages in that drawbacks caused by crystal lattice mismatch between the sapphire substrate and the GaN or InxGa1-xN crystal and a difference of expansion coefficients can be improved.
However, the AlN or GaN intermediate buffer layer grown on the sapphire substrate at a low temperature controls a crystal characteristics at a starting of crystallization, which in turn controls the GaN or InxGa1-xN crystal characteristics, which is grown thereafter. Because crystal defects of the GaN or InxGa1-xN grown on AlN or GaN are dependent on the initial crystal of the AlN or GaN grown on the sapphire substrate, particularly the large space between columnar crystals formed initially and the great crystallization stress coming from the comparatively strong crystal bonding force of the AIN or GaN controls an irregularity(i.e., spaces between respective microcrystals), crystalline, and a surface size of the column, of the initial columns of the AlN or GaN, the GaN or InxGa1-xN crystal defects has a high crystal defect concentration in a range of approx. 109/cm2, if the GaN or InxGa1-xN crystal is grown by using the AlN or GaN crystal on the sapphire substrate as an intermediate buffer layer.
Accordingly, the present invention is directed to a GaN system compound semiconductor and a method for growing a crystal thereof that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a GaN system compound semiconductor and a method for growing a crystal thereof, which can reduce a concentration of crystalline defects caused by lattice mismatch, significantly.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for growing a crystal of a GaN system compound semiconductor, including the steps of (1) providing a sapphire substrate, (2) crowing an intermediate buffer layer of InxAl1-xN on the sapphire substrate, and (3) growing GaN or InxGa1-xN system compound semiconductor on the intermediate buffer layer.
In other aspect of the present invention, there is provided a method for growing a crystal of a GaN system compound semiconductor, including the steps of (1) providing a sapphire substrate, (2) growing a superlattice structure of InxAl1-xxN/AlN or InxAl1-xN/GaN on the sapphire substrate as an intermediate buffer layer, and (3) growing a GaN system compound semiconductor of GaN or InxGa1-xN on the intermediate buffer layer.
In another aspect of the present invention, there is provided a GaN system compound semiconductor including a sapphire substrate, an intermediate buffer layer of InxAl1-xN grown on the sapphire substrate, and a GaN system compound semiconductor of GaN or InxGa1-xN grown on the intermediate buffer layer.
In further aspect of the present invention, there is provided a GaN system compound semiconductor including a sapphire substrate, a superlattice structure of InxAl1-x/AlN or InxAl1-xN/GaN grown on the sapphire substrate as an intermediate buffer layer, and a GaN system compound semiconductor of GaN or InxGa1-xN grown on the intermediate buffer layer.
By using InxAl1-xN or InxAl1-xN/GaN as an intermediate buffer layer, which has a lattice constant in the middle of a lattice constant of the GaN system compound semiconductor of GaN or InxGa1-xN intended to grow on a sapphire substrate, the GaN system compound semiconductor and the method for growing a crystal thereof of the present invention can overcome a great lattice mismatch between the substrate and the GaN system compound semiconductor which can not be sustained only by AlN, to reduce a concentration of crystalline defects caused by the lattice mismatch, significantly.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.